The present invention relates generally to fuel gas heating, and more particularly, to leveraging a thermal energy storage unit to heat fuel gas supplied to a gas turbine engine.
During operation, a gas turbine engine combusts a mixture of fuel gas and air to generate hot combustion gases which drive rotation of one or more stages of turbine blades. The rotation may be used to drive a load such as an electrical generator. Typically, when a gas turbine engine initially starts up, the fuel gas and air are mixed directly in the combustor chamber of the gas turbine engine. Eventually, as the load ramps up, the gas turbine engine will operate in a pre-mix combustion mode in which the fuel gas and air are mixed upstream of the combustor chamber. Harmful emissions containing mono-nitrogen oxides (NOx) are generally much higher during the initial startup of the gas turbine engine and will improve dramatically once a pre-mix combustion mode is initiated. Consequently, it is desirable to rapidly bring the gas turbine engine to a load level that operates in a pre-mix combustion mode in order to reach an NOx emissions level that is in compliance with pertinent regulations. The faster the gas turbine engine reaches a so-called “emissions-compliant” load level, the smaller is the total amount of harmful emissions.
The rate of loading of a gas turbine engine is generally dependent on a stable operation of the combustor chamber. The stable operation of the combustor chamber is primarily controlled by the fuel gas temperature. In particular, during startup, the gas turbine engine will cycle through several combustion modes before initiating a pre-mix combustion mode. These combustion modes including the pre-mix combustion mode each require a certain minimum fuel gas temperature at the inlet of the combustor chamber before it can sequence through the next mode.
Fuel gas heating systems are typically utilized during the startup of a gas turbine engine in order for it to more quickly meet fuel gas temperature requirements that are necessary for operating at a low-emissions operating load. One example of a fuel gas heating system includes using hot water generated from within other components used in a power plant in which the gas turbine engine operates in order to heat the fuel gas. The use of such a fuel gas heating system is limited by the ability of these power plant components to generate hot water in a timely and efficient manner. For example, during a power plant startup after a sufficiently long down time, it may take a significant amount of time before one of these power plant components can actually provide hot water at the temperatures needed for fuel gas heating to attain required temperature levels. In this instance, the gas turbine engine will have to idle at some part-load condition as the component warms up enough to provide the hot water temperatures that will enable sufficient fuel gas heating. Other examples of fuel gas heating systems include using auxiliary systems such as electric heating or an auxiliary boiler to heat the fuel gas. These types of fuel gas heating systems are typically expensive to deploy.